Ring seal assembly

ABSTRACT

A SEAL ASSEMBLY FOR A SHAFT AND A HOUSING WHEREIN ONE ROTATES RELATIVE TO THE OTHER INCLUDES A FILLED POLYTETRAFLUOROETHYLENE (PTFE) SEAL ELEMENT WHICH IS SPLIT AND INCLUDES FLEXIBLE AND MOVABLE OVERLAPPING FREE ENDS IN OPPOSED SEALING RELATION AT AMBIENT TEMPERATURE. AS THE TEMPERATURE INCREASES, THE SEAL ELEMENT TENDS TO GROW SO THAT ONE OF THE FREE ENDS SEALS AGAINST ONE OF THE RADIAL FACES OF THE SEAL ELEMENT. AS THE TEMPERATURE DROPS FROM AMBIENT THE SEAL CONTRACTS SO THAT THE OPPOSED FACES ARE IN SEALING ENGAGEMENT. THE SEAL IS ENERGIZED INTO SEALING ENGAGEMENT BY THE FLUID BEING SEALED. REFERENCE IS MADE TO APPLICATION SERIAL NO. 735,812, FILED OF EVEN DATE HEREWITH AND ASSIGNED TO THE SAME ASSIGNEE.

United States Patent [72] Inventor Frank J. Mastromatteo Dayton, Ohio[21] Appl. No. 735,811 [22] I Filed June 10, 1968 [45] Patented June28,1971 [73] Assignee The Duriron Company, lnc.

Dayton, Ohio [54] RING SEAL ASSEMBLY 10 Claims, 7 Drawing Figs.

[52] US. Cl 277/26, 277/59. 277/222 [51] 1nt.Cl Fl6j9/00, F02f5/00 [50]Field of Search 277/26, 222,59

[56] References Cited UNITED STATES PATENTS 3,259,392 7/1966 Peickii eta1. 277/177X 3,390,889 7/1968 Grover 277/l98 OTHER REFERENCES Journal ofTeflon, Vol. 6. No. 6, Aug. 1965, (pages 4 to 7) Piston Ring SealsofTeflon, by H. A. Traub Primary Examiner-Samuel B. RothbergAttorney-Marechal, Biebel, French & Bugg ABSTRACTrA seal assembly for ashaft and a housing wherein one rotates relative to the other includes afilled polytetrafluoroethylene (PTFE) seal element which is split andincludes flexible and movable overlapping free ends in opposed sealingrelation at ambient temperature. As the temperature increases, the sealelement tends to grow so that one of the free ends seals against one ofthe radial faces of the seal element. As the temperature drops fromambient the seal contracts so that the opposed faces are in sealingengagement. The seal is energized into sealing engagement by the fluidbeing sealed.

Reference is made to application Serial No. 735,812, filed ofeven dateherewith and assigned to the same assignee.

RING SEAL ASSEMBLY BACKGROUND OF THE INVENTION This invention relates toa seal assembly and more specifically to an improved seal assembly foruse over a wide tem perature range.

The use of fluorocarbon resins as seal elements is well known. Commonlyused materials are polytetrafluoroethylene and tetrafluoroethylene andhexafluoropropylene copolymers. The seal element, be it an O-ring orflat gasket-type ring or lip seal is usually urged into sealingengagement by a resilient energizing member, and the seal elementusually substantially completely fills the groove or recess in which itis received.

One of the problems associated with the use of fluorocarbon sealelements is the relatively high coefficient oflinear thermal expansion.For example, unfilled PTFE has a coefficient of 5.5xlahl in./in./ F. inthe range of 73 to 140 F., in the case of the copolymer, the value is4.6 to 5.8Xl0 in./in./ F. over the same temperature range. Using fillersreduces the effective coefficient to a value between about 3.8 to 45x10.for example. Thus, PTFE has a coefficient about times that of mostgrades of steel. In those instances in which the part is to be exposedto wide variations in temperature, e.g., 40 to 350 F. the lineal growthper inch over that range of temperature is about 0.0215 inch. For a sealelement of a 2-inch outside diameter, the total lineal growth over therange is 0.136 inch, or 0.043 inch diametrically for the range.

The difficulties associated with change in dimension of PTFE parts isfurther compounded by the fact that the linear coefficient of expansionvaries for different temperatures, e.g.

77 to 32F 11.1..10'

50 to 68 F 8. 9X10 68 to 77 F 43. 0X10" 77 to 86 F i 8. 9X10 T7 to 302 F7. 5X10 From this data it becomes clear the rate of growth over therange of 68 F. to 77 F. is significantly higher than the remaining rangeof temperature. The lineal growth over that range is 0.0039 inch perinch. Therefore, the same seal element supra, has a lineal growth of0.0285 inch in the range of 68 to 77 F., corresponding to a diametricalchange of 0.009 inch. This data is significant because it shows thatcooling a 2-inch seal element from 77 F. to 68 F, the diametricalshrinkage is approximately 0.009 inch.

One approach to limiting the effect in changes of seal dimension hasbeen to confine theseal element mechanically over the entire rangeoftemperatures so that the seal is unable to move. While such designsare effective, they are also complicated and expensive thus limiting theuse of PTFE to those installations in which no other material willoperate satisfactorily.

Another approach has been to proportion the seal element so that itseals efficiently at lower temperatures, and as the temperatureincreases, the dimension of the seal increases, and in some instancesdeforms or is wedged between the surface to be sealed so that it cannotcontract as the temperature is reduced. Ultimately, such a'seal becomesinefficient even at the higher temperature.

A typical example of a seal arrangement exposed to wide variations inboth temperature and pressure is the internal seals for hydraulicallycontrolled automatic transmissions for automobiles and the like. Thebasic elements ofa transmission of this type are: (l) a hydraulic torqueconverter, (2) a planetary gearset, (3) multiple-disc clutches, (4)sprag clutches, (5) bands, and associated valves, pumps and controlelements for flow of hydraulic fluid which controls the transmissionoperation. The hydraulic pressure may vary from zero to almost 200 psiwhile the temperature may vary from 40 F. to 350 F. Within thetransmission there are several seals, with adjacent seals defining thehydraulic flow path to various elements of the transmission. Forexample, there are two seals between the front plate of the pumpassembly and the forward clutch to control operation of the forwardclutch, and four seals forming three passageways between the supporthousing for the intermediate clutch and sprag and the direct clutchhousing. These three passages control operation of the direct clutch,the front band and the intermediate sprag.

Currently, the seals used are split metallic rings which permit someleakage offluid, but which are sufficiently tight to effect operation ofthe various clutches, bands and sprags. Since there is some loss ofpressure, the pump used to supply the pressure must be sufficientlylarge to provide the various pressures in addition to the pressure lostthrough seal leakage.

SUMMARY OF THE INVENTION In accordance with the present invention, arelatively simple seal assembly is provided which overcomes some of thedifficulties associated with the use of PTFE in seal assemblies, andwhich is effective as a sealing element without the use of an energizingmember and operates over a wide range of temperatures. Seal assembliesof the present invention are particularly useful in hydraulicallycontrolled automatic automotive transmissions wherein the hydraulicfluid to be sealed operates as the energizing medium to establish asealing relation through the seal element.

The seal assembly of the present invention includes a seal element ofPTFE material which is in the form of an annular split disc havingspaced radial faces, the outer periphery of the disc forming the sealingface. The seal element is received in a groove on the shaft, the innerperipheral dimension thereof being sufficiently larger than theperipheral dimension of the base of the groove on the shaft to form anannular chamber, the inner periphery of the seal element being spacedfrom the base of the groove. The seal element is a split disc havingmovable and flexible free ends which are in opposed overlapped sealingrelation at ambient temperatures. Each free end of the seal elementincludes an inclined face, which with the adjoining radial face forms anangle of 10 to l5 so that this section of the seal element is taperedand quite flexible. As the temperature increases above ambient, the sealelement tends to grow. Since it includes freely movable ends, the sealelement is free to grow and the opposed inclined faces are maintained insealing engagement by the fluid being sealed. Any portion of theinclined face which projects over the opposed radial face is deflectableinto sealing engagement therewith. As the temperature drops, the seal isfree to contract with the opposed inclined surfaces again in sealingengagement if fluid pressure is applied. The cross-sectional dimensionof the seal element is less than the width of the groove.

A seal is established by fluid under pressure, and as the fluid contactsthe seal ring, it forces one radial face of the seal element intoengagement with the groove wall, and enters between the inner peripheryof the seal element and the groove forcing the seal element outwardlyinto tight sealing engagement with the housing.

Accordingly, it is a primary object of the present invention to providean improved relatively simple seal assembly including a split type whichmay be energized to provide an efficient seal over a wide variety ofpressures and temperatures.

Another object of this invention is to provide a seal assembly of thetype described using a split PTFE seal element wherein the seal assemblyis particularly useful in hydraulically actuated automotivetransmissions of the automotive type.

Other objects and advantages of the present invention will be apparentfrom the following description, the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partly in section andpartly in elevation of the seal assembly of the present inventionpositioned on a rotating shaft;

FIG. 2 is a view in section taken along the lines 2-2 of FIG.

FIG. 3 is an enlarged fragmentary section taken along the lines 3-3 ofFIG. 2 showing the outer peripheral surface end of the seal element inaccordance with the present invention;

FIG. 4 is an enlarged fragmentary view of a portion of FIG. 2 showingthe relative position of portions ofthe seal element at temperaturesbelow ambient;

FIG. 5 is a view similar to FIG. 3 illustrating the relative position ofportions of the seal element at temperatures below ambient; and

FIGS. 6 and 7 are views similar to FIGS. 4 and 5, respectively,illustrating the relative position of portions of the seal element attemperatures above ambient.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, whichillustrates a preferred embodiment of the invention, a seal arrangementis shown for a rotatable shaft 10 positioned within a housing 11, theshaft being spaced from the housing as indicated by clearance 13therebetween. The shaft 10 is provided with spaced grooves 14 and I6,with the portion 17 of the shaft between the grooves forming a fluidflow channel. Positioned in each of the grooves M and I6 is a sealelement each of the same construction, although it is understood thatthe shaft may be provided with only one seal element, if a fluid flowchannel is not used.

Each seal element 25 is in the form of an annular fluorocarbon memberhaving spaced radial faces 25a and 25b, the seal member being split asindicated generally at 26. The outer peripheral surface 25c ofthe sealelement is in sealing engagement with the opposed wall ofthe housing 11.The dimensions of the seal element 25 are coordinated with thedimensions of the grooves 14 and 16 as follows-Each groove has a base 27of predetermined depth and sidewalls 27a and 27b spaced a predetermineddistance apart. The inner peripheral dimension of the seal element isless than the diameter of the shaft 10 but sufficiently greater than thediameter of the base 27 of the groove to form an annular clearance orchamber 23 between the base and the groove and the inner periphery ofthe seal. Proportioned as described, at least a portion of the radialfaces 25a and 25b of the seal elements overlaps a portion of the opposedspaced sidewalls 27a and 2712, respectively, of the groove. Thecross-sectional dimension of the seal element, that is, the dimension asmeasured between the radial faces is less than the cross-sectionaldimension or width of the groove as measured between the opposedsidewalls 27a and 27b. Preferably, the cross-sectional dimension of theseal element is at least 50 percent and preferably 60 percent that ofthe groove to prevent it from cocking or being distorted in the groove.Thus, the seal element is capable of limited lateral movement along theaxis ofthe shaft 10.

Referring to FIGS. 2 and 3, it can be seen that the seal element 25 issplit at 26 to provide free ends 29 and 30. The split is made by cuttinga continuous seal blank, after it is formed by conventional PTFEprocessing, by bias cutting from the outer to the inner periphery orvice versa at a particular angle relative to the plane of the seal aswill be described more fully below.

At ambient temperatures, the flexible and movable free ends of the sealwhich include inclined faces 2% and 30a are positioned in opposed facingand overlapped relation, as shown and care should be taken uponinstallation to assure that the faces 29a and 30a are in the relativeposition shown in FIG. 3. The angle between the inclined face and theadjoining radial face, that is, between faces 25b and 30a, and between25a and 29a is less than 45 and preferably between 10 and l5 in order toprovide readily flexible free ends which are easily responsive to fluidpressure so that the ends are maintained in sealing engagement with eachother upon application of pressure.

The operation of the seal assembly under fluctuations in temperature canbe understood with reference to FIGS. 4 and 5. As the temperature of theseal decreases, the free ends 29 and 30 are free to move so that the tipend 2% of end 29 is spaced from the junction 30b between radial face 250and the inclined face 30a. Similarly the tip end 30c of end 30 is spacedfrom the junction 290 between radial face 25b and inclined face 29a.

As the temperature of the seal assembly increases, the ends of the sealpass through the relative position shown in FIGS. 2 and 3. As thetemperature increases further, the ends of the seal assume the relativepositions generally shown in FIGS. 6 and 7 wherein the same referencenumerals have been used. At temperatures above ambient, the tip end 29bof end 29 extends beyond junction 290 while a portion of each of theinclined faces remain in overlapped relation and the tip portion of face29 is sealed against radial face 250. Depending on the amount of growthof the seal element, tip end 300 of end 29 may or may not extend beyondjunction 290, although shown that way in FIG. 6 for purposes ofillustration.

Typical dimensions of the seal assembly of the present invention are asfollows: Assuming a groove dimension of 0.095 inch depth and 0.095 inchwidth, the seal element is a crosssectional dimension of between 0.096inch to 0.102 inch between its inner and outer peripheral surfaces. Thedimensions between the radial faces is between 0.060 inch to 0.065 inch.The clearance between the inside periphery 28 of the seal element andthe base of the groove 27 is approximately 0.015 inch. The angle betweenthe inclined face and the radial face is l2+l2. Assuming a seal ringhaving a 2-inch inside diameter, the total lineal growth in the range of68 to 77 F. is approximately 0.0285 inch. Since a lineal change of0.0285 inch represents a diametrical change of about 0.009, it ispreferred that upon installation, there be a tight fit, and preferablythe interference fit with the ring being a few thousandths of an inchand possibly 0.010 of an inch greater than the dimension of the housing.In this way, as the seal element contracts, it remains in sealingengagement as described. As the temperature begins to increase, the sealelement grows, that is, expands both in circumference and in crosssection so that sealing pressure is maintained at the highertemperature.

The operation of the seal may be understood with reference to FIGS. 1and 5, the latter showing the flow path of fluid which is to be sealedagainst. Fluid flowing through chamber 17 passes between the shaft andthe housing and contacts the face 25a of the seal element forcing theopposite face 25b into contact with sidewall 27a of the left groove orsidewall 27b of the right groove. Additionally, fluids flows into thechamber 28 and acts on the inside peripheral surface of the seal elementto force it radially outwardly towards the housing, and thus forcing theoutside peripheral surface of the seal element in tight sealingengagement with the housing.

In the case of a transmission of the type described, at coldtemperatures, the hydraulic fluid is generally quite viscous so thateven if the seal assembly has contracted substantially, there is verylittle leakage of fluid between the seal element and the housing. As thetemperature of the hydraulic fluid increases, the seal element expandsand seals it tightly.

A seal assembly of the type herein described is quite effective inautomotive transmissions of the type described particularly because ofthe ability to seal in response to different pressures, which in thecase of automotive transmission may vary from 0 to well over 200 psi; Acomparative test of the seal element of the type described against solidseal elements without an energizer, or split seal elements, or lap sealelements indicates that the seal element of the present invention isconsiderably more efficient at the lower temperatures. Seal assembliesin accordance with the present invention operated quite satisfactorilyin a static and dynamic seal test and at temperatures as low as -40, andat temperatures as high as 300 F.

It is preferred in accordance with the present invention that the sealelement be of polytetrafluoroethylene, preferably filled with a finelydivided material such as glass, molybdenum, graphite, bronze, cokeflour, asbestos, copper or mixtures thereof. A particularly good sealelement has been obtained with the use of finely divided glass presentin an amount of 15 percent by weight. In view of the high temperaturecapability of polytetrafluoroethylene as opposed to the fluorocarboncopolymer previously mentioned, polytetrafluoroethylene offers adistinct advantage.

While the form of apparatus herein described constitutes a preferredembodiment of the present invention, it is to be understood that thisinvention is not limited to this precise form of apparatus and thatchanges may be made therein without departing from the scope of theinvention which is defined in the appended claims.

I claim:

1. In a seal assembly for use over a wide range of temperaturesestablishing and maintaining a seal between a shaft and a housing oneofwhich is rotatable relative to the other by being energized intosealing engagement solely by the fluid to be sealed, said housing andshaft having a coefficient of thermal expansion different from the sealelement, and wherein said shaft includes groove means having a base of apredetermined depth and sidewalls spaced a predetennined width forreception of said seal assembly, the improvement comprising a splitannular fluorocarbon seal element having spaced radial faces receivedwithin said groove means and having an outer peripheral surface insealing contact with said housing, the inner peripheral dimension ofsaid seal element being less than the diameter of said shaft and greaterthan the diameter of the base of said groove to provide an overlappingarea between said radial faces and the opposed sidewall while providingan annular chamber between the inner peripheral surface of said sealelement and the base of said groove, the cross-sectional dimension ofsaid seal element being less than the width of said groove so that fluidpressure is operative to urge one of said radial faces into sealingengagement with the opposed sidewall in said overlapping areas, saidsplit seal element including flexible and movable free ends which are inopposed overlapped relation at ambient temperatures, each free end ofsaid seal element including an inclined face forming an angle of lessthan 45 with the adjoining radial face, said seal element tending tocontract in response to reduction in temperature from ambienttemperatures whereby at least one of said LII free ends is in opposedrelationship with the adjoining radial face, said seal element tendingto expand in response to increase in temperature above ambienttemperature whereby at least one of said free ends is in opposed sealingrelationship with the opposed inclined face of the other free end ofsaid seal element.

2. The seal assembly as set forth in claim 1 wherein said seal elementis polytetrafluoroethylene.

3. The seal assembly as set forth in claim 1 wherein said seal elementis polytetrafluoroethylene filled with a material selected from thegroup consisting of glass, molybdenum, graphite, bronze, coke flour,asbestos, copper and mixtures thereof.

4. The seal assembly as set forth in claim 2 wherein saidpolytetrafluoroethylene is filled with 15 percent glass.

5. The seal assembly as set forth in claim 1 wherein the angle betweenthe inclined face and the adjoining radial face of each free end is thesame.

6. The seal assembly as set forth in claim 1 wherein the cross-sectionaldimension of said element is at least 50 percent the width of saidgroove.

7. The seal assembly as set forth in claim 5 wherein the angle betweenthe inclined face and the adjoining radial face of each free end isbetween 10 and 15.

8. A sea] assembly as set forth in claim 7 wherein the crosssectionaldimension of said seal element is at least 60 percent of the width ofsaid groove.

9. A seal assembly as set forth in claim 7 wherein said seal element isof polytetrafluoroethylene filled with 15 percent by weight ofparticulate finely divided glass.

10. A seal assembly as set forth in claim 1 wherein said shaft includesmultiple spaced said grooves, each said groove including one of saidseal elements.

